全文获取类型
收费全文 | 627篇 |
免费 | 18篇 |
国内免费 | 6篇 |
专业分类
化学 | 345篇 |
力学 | 57篇 |
数学 | 114篇 |
物理学 | 135篇 |
出版年
2023年 | 5篇 |
2022年 | 14篇 |
2021年 | 22篇 |
2020年 | 17篇 |
2019年 | 17篇 |
2018年 | 13篇 |
2017年 | 10篇 |
2016年 | 33篇 |
2015年 | 20篇 |
2014年 | 16篇 |
2013年 | 34篇 |
2012年 | 41篇 |
2011年 | 48篇 |
2010年 | 23篇 |
2009年 | 21篇 |
2008年 | 43篇 |
2007年 | 22篇 |
2006年 | 32篇 |
2005年 | 21篇 |
2004年 | 27篇 |
2003年 | 15篇 |
2002年 | 11篇 |
2001年 | 12篇 |
2000年 | 8篇 |
1999年 | 7篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1991年 | 5篇 |
1990年 | 9篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1974年 | 4篇 |
1973年 | 6篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1967年 | 2篇 |
1966年 | 2篇 |
1958年 | 2篇 |
排序方式: 共有651条查询结果,搜索用时 15 毫秒
191.
Osmotic pressures of aqueous solutions of poly(diethylaminoethyl methacrylate) hydrochloride, in equilibrium with a precipitate of the un-ionized polybase, at various concentrations of polymer and NaCl in solution and at different values of pH are derived from emf measurements and the “cell” theory for polyelectrolytes. Single-ion activities are evaluated according to two procedures. The first is based on measurements with ion-specific electrodes versus a calomel electrode. The second makes use of a salt bridge, but assumes that the co-ions have activity coefficients equal to the mean activity coefficient of the salt in a polyelectrolyte-free solution of the same concentration. The results show that the calculated values of the osmotic pressures are consistent with those obtained by the exact integration of the Gibbs-Duhem relationship, when the first procedure is employed. If, however, the single-ion activities are evaluated by the second procedure, the osmotic pressures obtained are consistently lower by about 10%. These differences arise because the two methods yield different values of the activity coefficients of the single ions. 相似文献
192.
A general stream of n types of customers arrives at a Single Server station where service is non-preemptive, the server may undergo Poisson breakdowns and insertion of idle times is allowed. If ξ(k) and c(k) are, respectively, the expected service time and sojourn cost per unit time of a type k customer (1?k?n), call k “V.I.P.” type if ξ(k)/c(k) = min1?i?n[ξ(i)/sbc(i)].We show that any right-of-way service policy can be improved by a policy that grants V.I.P. customers priority over all others, and never inserts idle time when a V.I.P. customer is present.We further show that if the arrival stream is Poisson, the so-called “cμ” priority rule (applied with no delays) is optimal in the class of all service policies, and not just among those of a priority nature. 相似文献
193.
Dickson JL Ortiz-Estrada C Alvarado JF Hwang HS Sanchez IC Luna-Barcenas G Lim KT Johnston KP 《Journal of colloid and interface science》2004,272(2):444-456
The critical flocculation density (CFD), that is, the CO(2) density below which flocculation occurs, was studied for dilute water-in-CO(2) (W/C) miniemulsions stabilized with poly(1,1-dihydroperfluorooctyl methacrylate)-b-poly(ethylene oxide) (PFOMA-b-PEO) surfactants. The CFD, which was measured by turbidimetry, decreased as the PFOMA molecular weight was increased, the average droplet size was decreased, the surfactant loading was increased, and the temperature was increased. A simple model, which addressed both the van der Waals attraction between droplets and osmotic solvent-tail interactions, was in good qualitative agreement with the experimentally observed trends for the CFD and predicted a decrease in emulsion stability as the CO(2) density was lowered toward the theta density for PFOMA in bulk CO(2). 相似文献
194.
The synthesis of trimethylsilyl (TMS) hydroperoxide derivatives for gas chromatography (GC) was studied using N-methyl-N-(trimethylsilyl) trifluoroacetamide (MSTFA) for derivatization of cumene hydroperoxide (CMOOH) (alpha,alpha'-dimethylbenzyl hydroperoxide) and alpha-methoxyalkyl hydroperoxides formed by liquid- and gas-phase ozonolysis of a series of terminal alkenes in the presence of methanol (CH3OH). Derivatization efficiencies >90% were achieved over a wide range of solution concentrations. The major compounds identified by GC-mass spectrometry of the derivatized products of alkene-O3 reactions were alpha-methoxyalkyl hydroperoxides, methyl esters, and aldehydes. Yields of alpha-methoxyalkyl hydroperoxides and methyl esters were quantified using effective carbon numbers (ECNs) and used to determine the yields of stabilized Criegee intermediates (SCIs) from gas-phase ozonolysis reactions. Such measurements are important for understanding the atmospheric chemistry of alkene emissions. SCI yields measured for the reactions of 1-octene [CH3(CH2)5CH=CH2], 1-nonene [CH3(CH2)6CH=CH2 ], and 2-methyl-1-octene [CH3(CH2)5C(CH3)=CH2] are consistent with previous measurements or predictions based on literature data. SCI yields measured for the reactions of 1-decene [CH3(CH2)7CH=CH2], 1-dodecene [CH3 (CH2)9CH=CH2], and 1-tetradecene [CH3(CH2)11CH=CH2] are much lower than expected, apparently due to side reactions with low volatility aldehydes that form peroxyhemiacetals, which are not amenable to GC analysis. In general, the results indicate that off-line MSTFA derivatization can be an efficient means for increasing the stability of thermally labile hydroperoxides for identification and quantitation by GC, and offers a new approach for the analysis of these environmentally important compounds. 相似文献
195.
The main goal of the article is to show that Paley-Wiener functions ƒ ∈ L
2(M) of a fixed band width to on a Riemannian manifold of bounded geometry M completely determined and can be reconstructed
from a set of numbers Φi (ƒ), i ∈ ℕwhere Φi
is a countable sequence of weighted integrals over a collection of “small” and “densely” distributed compact subsets. In particular, Φi, i ∈ ℕ,can be a sequence of weighted Dirac measures δxi, xi ∈M.
It is shown that Paley-Wiener functions on M can be reconstructed as uniform limits of certain variational average spline
functions.
To obtain these results we establish certain inequalities which are generalizations of the Poincaré-Wirtingen and Plancherel-Polya
inequalities.
Our approach to the problem and most of our results are new even in the one-dimensional case. 相似文献
196.
Akerib DS Alvaro-Dean J Armel-Funkhouser MS Attisha MJ Baudis L Bauer DA Beaty J Brink PL Bunker R Burke SP Cabrera B Caldwell DO Callahan D Castle JP Chang CL Choate R Crisler MB Cushman P Dixon R Dragowsky MR Driscoll DD Duong L Emes J Ferril R Filippini J Gaitskell RJ Haldeman M Hale D Holmgren D Huber ME Johnson B Johnson W Kamat S Kozlovsky M Kula L Kyre S Lambin B Lu A Mahapatra R Manalaysay AG Mandic V May J McDonald R Merkel B Meunier P Mirabolfathi N Morrison S Nelson H Nelson R 《Physical review letters》2004,93(21):211301
We report the first results from a search for weakly interacting massive particles (WIMPs) in the Cryogenic Dark Matter Search experiment at the Soudan Underground Laboratory. Four Ge and two Si detectors were operated for 52.6 live days, providing 19.4 kg d of Ge net exposure after cuts for recoil energies between 10 and 100 keV. A blind analysis was performed using only calibration data to define the energy threshold and selection criteria for nuclear-recoil candidates. Using the standard dark-matter halo and nuclear-physics WIMP model, these data set the world's lowest exclusion limits on the coherent WIMP-nucleon scalar cross section for all WIMP masses above 15 GeV/c2, ruling out a significant range of neutralino supersymmetric models. The minimum of this limit curve at the 90% C.L. is 4 x 10(-43) cm2 at a WIMP mass of 60 GeV/c2. 相似文献
197.
198.
199.
200.